Sealing means for a reservoir for a liquefied gas



Filed June 25, 1964 Dec. 5, 1967 w, HAMILTON ET AL 3,355,892

SEALING MEANS FOR A RESERVOIR FOR A LIQUEFIED GAS 2 Sheets-Sheet 1 Dec. 5, 1967 w, HAMILTON ET AL 3,355,892

SEALING MEANS FOR A RESERVOIR FOR A LIQUEFIED GAS Filed June 25, 1964 2 Sheets-Sheet 2 United States Patent 3,355,892 SEALING MEANS FOR A RESERVOIR FOR A LIQUEFIED GAS William Hamilton, Frimley Green, near Aldershot, and Robert Glover Jackson, Hornchurch, Essex, England, assignors to Conch International Methane Limited, Nassau, Bahamas, a Bahamian company Filed June 25, 1964, Ser. No. 377,959 Claims priority, application Great Britain, Oct. 24, 1963, 42,094/63 8 Claims. (Cl. 61-.5)

This invention relates to a sealing means suitable for use in a reservoir for storing a liquefied gas.

The sealing means of this invention can be used either as an extension of a reservoir, particularly a ground reservoir, or it may be used as the lining itself, particularly as a lining for a ground reservoir in places where there is no aquiferous formation, and hence no possibility of a frozen liquid forming a light-tight seal in the earth formation surrounding the reservoir. In both cases the sealing means can act as a gas seal between the roof and the reservoir.

According to this invention sealing means for use in a reservoir for storing a liquefied gas comprises a continuous fluid-impervious membrane having vertical corrugations extending from the bottom of the membrane to the upper region of the membrane and horizontal corrugations in the upper region of the membrane above the vertical corrugations, a plurality of vertical structural members which are secured to the outside of the membrane at lines defining the troughs or crests of the vertical corrugations and which are spaced at intervals close enough for the membrane to be stable against hydrostatic forces exerted thereon and wherein the lower end of the membrane extends into a region which contains a material which is liquid at ambient temperature but which is solid when the membrane is in contact with a liquefied gas.

In this specification the term liquefied gas means a liquid which boils at atmospheric pressure at a temperature below the ambient temperature. Examples of liquefied gases are liquefied nitrogen, liquefied air, liquefied methane, liquefied natural gas, liquefied oxygen and liquefied propane.

In FIG. 1, a side elevation along the line A-A in FIG. 2 of sealing means acting as an extension to a ground reservoir is shown.

In FIG. 2, a plan view of part of the membrane and its attachment to a surrounding cylindrical wall is shown.

In FIG. 3, a cross-section of the modified I-beamacting as a structural member for the membrane is shown.

The membrane, that is material shown at 5, 15 in the figures which itself is of insufiieient strength to support loads to which it is subjected, is preferably metal. When it will be in contact with a liquefied gas the metal should be one which will not become embrittled at the low temperatures to which it is subjected. Examples of suitable metals, and metals which are suitable for contact with liquefied methane, are stainless steel, aluminium, aluminium alloys, copper or high nickel steels.

The membrane should be continuous, that is it should completely enclose an area. In most cases the membrane will be cylindrical, but it could for example enclose areas which are ellipses, squares, or rectangles.

The membrane 5 has vertical corrugations and the membrane at 15has horizontal corrugations, and in this specification, the terms vertical and horizontal are not to be construed in their strict geometrical sense. The vertical corrugations should extend nearly to the top of the sheet, and in any case above the level of liquid in the reservoir. The ratio of the pitch to the amplitude of the vertical corrugations depends on the load on the membrane and its thickness. For a given load one can either have a low pitch to amplitude ratio and a relatively thick membrane, or a higher pitch to amplitude ratio for a thinner membrane. For a ground reservoir for storing liquefied natural gas of depth 275 cm. typical dimensions for an aluminum membrane would be thickness 2.2 mm., pitch 12.7 cm. and amplitude cm.

The horizontal corrugations are needed at the top of the membrane to allow for dimensional changes of the membrane in the vertical direction. These corrugations need only be few in number for example two or three, and the rate of pitch to amplitude can be for example between 1:1 and 1:2.

The vertically corrugated portion of the membrane i.e. the fluted skirt, could, if the reservoir is small enough, be made in one piece with one welded join running parallel to the direction of corrugation. Preferably however it is made in more than one piece, especially in sheets which are welded together so that the welds run along each trough of the corrugations as viewed from inside the membrane. The horizontally corrugated portion of the membrane i.e. the corrugated collar, could also be made in one piece with one welded join running transverse to the corrugations. However in practice, except for very small reservoirs, it is necessary to make the corrugated collar in several pieces with welded joins preferably running transverse to the corrugations.

It is necessary to join the skirt to the collar, preferably by welding. To do this, pieces of sheet, preferably of the same material as the membrane, are welded to the tops of and at right angles to the corrugation-s of the skirt. The collar is then welded to these pieces of sheet. If for example the liner is cylindrical, and the skirts corrugations are curved, then these pieces of sheet will be shaped as segments of a circle. As an alternative to welding separate pieces of sheet, the upper edge of the skirt can be made undulated, the amplitude of the undulations corresponding to the amplitude of the corrugations of the skirt, and the projecting ends of the skirt being bent outwardly and then welded to the collar. Of course other methods can be used to weld the collar to the skirt so that a fluid-tight join is obtained, but so that the combined collar and skirt is not under undue stress at any tempera ture to which it is subjected.

The structural members 8 outside the membrane are preferably of the same material as the material of which the membrane is made. Alternatively they could be of a different material if said material had the same coefficient of thermal expansion and the two materials could be secured together e.g. by welding. The structural members are secured to the outside of the skirt of the membrane, and must extend to above the level of liquid in the reservoir. Preferably they extend the whole length of the skirt, but if desired they may taper oil towards the top and bottom of the skirt. The structural members are preferably secured to the troughs of the vertical corrugations when viewed from the inside of the membrane but could be connected to the crests of the corrugations when viewed from the inside of the membrane. Unless the amplitude of the corrugations is quite small, the vertical structural members are usually secured to each successive trough or crest.

The structural members 8 are preferably I-shaped beams, particularly modified I-beams in which each of the two feet of the I have recesses for reception of the adjacent sheets of the membrane. The feet are also preferably bent inwards, so that the curved membrane sheets between adjacent structural members do not have sharp bends. The preferred method of securing the structural members to the membrane is by welding. When the preferred form of I-beams is used the membrane sheets are inserted in the recesses, and they are then welded to the I-beams.

If desired the fluted skirt may also be reinforced with stitTeners. These stiifeners are preferably a series of metal ribs running round the inside of the membrane, which are substantially at right angles to the direction of the corrugations. These ribs are preferably welded to the membrane.

In order to stabilise the position of the membrane it is preferable if it is attached to supporting members e.g. supporting columns, situated outside the membrane. In the embodiment of the invention when the membrane is cylindrical, there is a cylindrical concrete wall 3 of larger diameter than the membrane outside the membrane and this wall has inwardly and vertically disposed ribs 4 at regular intervals. These ribs are spaced so that they coincide with each structural member attached to the skirt. Alternatively the concrete ribs members can be horizontally disposed e.g. horizontal ribs running right round the membrane.

The membrane is preferably connected to the supporting members e.g. ribs, by means of metal brackets which are welded to the structural members and the supporting members. A preferable method is to fix a metal lug to the structural member and metal brackets 11 to a supporting column (or vice-versa) so that they overlap and drive a fastening pin 12 through the lug and brackets so that they are both pivoted about the pin. The holes in the lug or in the brackets should preferably be slotted to allow for relative horizontal movement. For each structural member there are preferably at least two fastening members, one being near the top of the fluted skirt, and the other being some way from the bottom of the fluted skirt so as to allow for some lateral displacement of said bottom. If the fluted skirt is very short it is often possible to have only one fastening member per structural member, the fastening member being near the top of the fluted skirt.

In order that the lower end of the membrane may be sealed into the surrounding formation, said lower end can extend into a continuous gutter 6, which gutter contains a material 7 which is liquid at ambient temperature but which will be solid when the membrane is in contact with a liquefied gas. When the sealing means is used in a ground reservoir the continuous gutter is preferably formed in the ground as a channel or trench and is of dimensions suitable to receive the lower end of the fluted skirt. In certain circumstances however it may be desirable to use a metal or wooden trough as the gutter.

Alternatively, the lower end of the membrane may extend into liquid pervious substance e.g. detritus such as sand or gravel. In some cases the membrane at first just rests on the ground and then the ground surrounding the bottom of the membrane can be built up with a liquid pervious substance such as sand or gravel. The liquid pervious substance contains material which is liquid at ambient temperature but which is solid when the membrane is in contact with a liquefied gas, e.g. water.

The material liquid at ambient temperature must be solid at the temperature of the gutter walls or pervious layer when the reservoir is in use. Clearly this temperature is dependent on the stored liquid, the distance between the bottom of the membrane and the reservoir, and time. Care must be taken in selecting a liquid which will not freeze too soon, so that undesirable high stresses are not imposed on the membrane before it has reached its equilibrium temperature, and hence its equilibrium position.

If the ground reservoir is used for liquefied natural gas, suitable liquids which can be used are those having a freezing point of about but not below -90 C., e.g. nheptane, n-octane, n-butanol, the monoethyl either of ethylene glycol, ethyl acetate, isopropanol and various mineral oil fractions. If n-propane is being stored, suit- 4 able liquids for use in the gutter are those having a freezing point of about, but not below, l0 C., e.g. suitable mixtures of water with ethylene glycol or isopropanol. In some cases, water or waxy mineral oils may be used.

If however the inner face or both faces of the lower portion of the membrane are covered with a layer of fluid-impermeable readily deformable material e.g. polyethylene foam or polyvinylchloride foam, it is always possible to use any liquid which freezes below ambient temperature such as water. This is because with the layer on the inner face of the lower portion of the membrane there is no danger of high stresses being imposed on the membrane before the membrane has reached its equilibrium temperature.

Suitable ground reservoirs in which the sealing means can be used are holes in the surface of the earth which holes are impervious to the substance to be stored. Such holes are preferably those wherein the ground formation surrounding the hole contains a liquid e.g. water, which will solidify when the reservoir is charged with the substance to be stored. These reservoirs may if desired have a thick concrete lining to the side Walls of the hole. In such reservoirs wherein the walls are impervious to the substance being stored, the sealing means need only be situated at the top of the reservoir thereby acting as an extention to the reservoir up to the roof level. The top of the corrugated collar can be readily fixed to the periphery of the roof, thus enabling the sealing means to form a gastight seal for the reservoir in addition to forming the top part of the reservoir.

The sealing means however is eminently suitable for use in ground reservoirs wherein the side walls would otherwise be permeable to the substance to be stored. In such reservoirs, e.g. ground reservoirs which are holes in the surface of the earth, the membrane acts as a lining and extends right down the sides of the reservoir and is received at the bottom of the reservoir in a region containing the material liquid at ambient temperature. In such cases, however, the bottom wall must be impervious to the substance to be stored. This can in many cases be made impervious by covering the bottom with a layer of clay. The top of the membrane is fixed to the periphery of the roof so that the lining also acts as a gas seal.

The sealing means of this invention whether used in only the top portion reservoir or throughout the whole depth of the reservoir, can of course be used in reservoirs other than the ground reservoirs specifically mentioned above, i.e. they could be used in land storage tanks, that is tanks constructed above the ground.

As mentioned above the sealing means of this invention can be connected to the roof so that it acts as a gas seal. This is achieved by welding or otherwise securing the top portion of the corrugated collar of the membrane to the periphery of the roof. A suitable roof for use in conjunction with the sealing means is one comprising a fiat or cambered sheet lined on at least one surface with thermal insulation, a superstructure from which the sheet is suspended, and a counterweight acting on said sheet. The sheet may be suspended from the superstructure by means of hangers flexible in the horizontal direction, and the counterweight may comprise blocks of concrete resting on the sheet.

An embodiment of the invention is now described with reference to the accompany drawings.

Referring to FIGURES 1, 2 and 3 of the drawings, a hole 1 is dug into the ground 2. The top edge of the hole 1 is stepped so as to allow a cylindrical wall 3 to be built. This wall has inwardly and vertically extending ribs 4 spaced at intervals corresponding to the troughs in the corrugated aluminium membrane 5. Inside the wall 3 and the ribs 4 an annular channel 6 is dug. This channel 6 contains water 7 which eventually freezes when the reservoir is in use.

The separate sheets of the membrane 5 are welded at 9 to I-beam sections 8. Lugs 10 are attached to the I-beams 8 and these lugs 10 are pivoted about pins 12 so that they are connected to pairs of brackets 11 attached to the ribs 4. The holes in the lugs 10 are slotted in the horizontal direction to allow for relative movement between the lugs and brackets. The membrane sheets are also strengthened by light aluminium sections 13 welded to the inner surface of the membrane. To the lower end of the membrane are attached strips of low modulus polyvinyl chloride foam 14. This prevents excessive stresses being exerted on the membrane when the water 7 freezes. The corrugated collar 15 is welded to the top of the sheets 5 via segmental strips 16 to make a fluid impervious membrane. The top of this collar is welded to the roof comprising horizontal beams 25, top sheet 17 and insulation 18 carried on expanded aluminium sheet 19. The collar 15 is welded to the roof so as to make a gas-tight seal for the top of the reservoir.

On top of the wall 3 are piers 20 to which is anchored at 21 one of the ribs 22 constituting the superstructure. The roof is suspended from the superstructure by means of hangers 23. Concrete blocks 24 rest on pedestals 26, thereby counteracting any upward thrust on the top sheet 17.

We claim:

1. Sealing means for use in a ground reservoir having a main storage cavity and a roof for storing a liquefied gas comprising a continuous fluid-impervious membrane defining an enclosing sidewall of said cavity, said membrane being of insufficient strength and rigidity to form a self-supporting tank and having vertical corrugations extending from the bottom of the membrane to the upper region of the membrane and horizontal corrugations in the upper region of the membrane above the vertical corrugations, the top line of said membrane being sealed to the roof of the reservoir, a plurality of vertical elongated stifiening members which are slidably secured to the outside of the membrane at respective vertical lines of the vertical corrugations and which are of sufiicient length spaced at intervals close enough for the membrane to be stable against hydrostatic forces exerted thereon, fixed rigid supporting means external to said membrane supporting said roof, expansion-joint supporting means securing said stiffening members to said fixed supporting means and a peripheral gutter region into which the lower end of the membrane extends, which gutter region contains a material which is liquid at ambient temperature but which is solid when the membrane is in contact with a liquefied gas.

2. Sealing means as claimed in claim 1 wherein at least the inner face of the lower portion of the membrane is covered with a layer of fluid impermeable, readily deformable material.

3. Sealing means as claimed in claim 1 wherein the material liquid at ambient temperature but solid when the membrane is in contact with a liquefied gas is water.

4. Sealing means as claimed in claim 1 wherein the material in the gutter comprises a mixture of liquid and a liquid pervious substance.

5. Sealing means as claimed in claim 1 wherein the vertically corrugated portion of the membrane comprises metal sheets which are welded together so that the welds run along each line of the corrugations as viewed from the inside of the membrane.

6. Sealing means as claimed in claim 5 wherein the stiffening members are modified I-beams comprising a Web member and two transverse end members in which one of the end members has recesses for the reception and support of adjacent sheets which constitute the membrane and in which said recesses are bent so as to be in the plane of the membrane.

7. For use in a ground reservoir for liquefied gas with an above-ground roof, sealing means between the walls of the reservoir and the ground comprising (a) a peripheral ground-supported wall surrounding said reservoir and supporting said roof,

(b) a continuous fluid-impervious sealing membrane, of insufiicient strength to support by itself the fluid load to which it is subjected surrounding the top of said reservoir between the inside of, and spaced from, said wall and extending in sealing relation from said reservoir to said roof,

(c) said membrane having a series of vertical corrugations extending from the bottom of the membrane to the upper region thereof, and horizontal corrugations in the upper region of the membrane above the vertical corrugations,

(d) a plurality of vertical elongate stiffening members secured to said membrane at respective vertical lines of said corrugations and slidably supported by said wall, said members being spaced sufiiciently close to gether and of length for the membrane to be stable against hydrostatic forces exerted thereon by liquid in the tank,

(e) a peripheral trench surrounding the top of the reservoir inside of said wall, the lower end of said membrane extending into said trench,

(f) a vapor-sealing material in said trench which is liquid at ambient temperature, but which is solid when the reservoir contains liquefied gas.

8. Sealing means as claimed in claim "7, said wall being of concrete, and a series of concrete vertical ribs extending inwardly from said wall, and supporting means extending from said ribs to respective ones of said vertical structural members for supporting same.

References Cited UNITED STATES PATENTS 1,151,184 8/1915 Hurlbrink 220 1,864,931 6/1932 Pritchard 220 -72 X 2,478,731 8/1949 Wiggins 48-178 2,924,350 2/1960 Greer 220-18 X 3,096,902 8/1963 Schroeder 220-18 3,047,184 7/1962 Van Bergen et a1 220-9 3,085,708 4/1963 Dosker 220-9 3,093,935 6/1963 Dunn 52-309 3,151,416 10/1964 Eakin et al. 61.5 X 3,195,310 8/1965 Schroeder 61.5 3,196,622 7/1965 Smith et al 62-45 3,205,665 9/1965 Van Horn 61.5

FOREIGN PATENTS 921,844 3/1963 Great Britain.

EARL J. WITMER, Primary Examiner. 

1. SEALING MEANS FOR USE IN A GROUND RESERVOIR HAVING A MAIN STORAGE CAVITY AND A ROOF FOR STORING A LIQUEFIED GAS COMPRISING A CONTINUOUS FLUID-IMPERVIOUS MEMBRANE DEFINING AN ENCLOSING SIDEWALL OF SAID CAVITY, SAID MEMBRANE BEING OF INSUFFICIENT STRENGTH AND RIGIDITY TO FORM A SELF-SUPPORTING TANK AND HAVING VERTICAL CORRUGATIONS EXTENDING FROM THE BOTTOM OF THE MEMBRANE TO THE UPPER REGION OF THE MEMBRANE AND HORIZONTAL CORRUGATIONS IN THE UPPER REGION OF THE MEMBRANE ABOVE THE VERTICAL CORRUGATIONS, THE TOP LINE OF SAID MEMBRANE BEING SEALED TO THE ROOF OF THE RESERVOIR, A PLURALITY OF VERTICAL ELONGATED STIFFENING MEMBERS WHICH ARE SLIDABLY SECURED TO THE OUTSIDE OF THE MEMBRANE AT RESPECTIVE VERTICAL LINES OF THE VERTICAL CORRUGATIONS AND WHICH ARE OF SUFFICIENT LENGTH SPACED AT INTERVALS CLOSE ENOUGH FOR THE MEMBRANE TO BE STABLE AGAINST HYDROSTATIC FORCES EXERTED THEREON, FIXED RIGID SUPPORTING MEANS EXTERNAL TO SAID MEMBRANE SUPPORTING SAID ROOF, EXPANSION-JOINT SUPPORTING MEANS SECURING SAID STIFFENING MEMBERS TO SAID FIXED SUPPORTING MEANS AND A PERIPHERAL GUTTER REGION INTO WHICH THE LOWER END OF THE MEMBRANE EXTENDS, WHICH GUTTER REGION CONTAINS A MATERIAL WHICH IS LIQUID AT AMBIENT TEMPERATURE BUT WHICH IS SOLID WHEN THE MEMBRANE IS IN CONTACT WITH A LIQUEFIED GAS. 